Mechanical Joint Retainer Glands are designed to provide a method for restraining mechanical joint pipe and fittings and other standardized mechanical joints against possible joint separation, rupture or blow-out caused by internal water.
So a mechanical joint retainer gland assembly is a restrained joint and would not require a thrust block at the location of the assembly.
Is it common to still use mechanical joint retainer glands underground (fire line)? I saw that US Pipe recommended against retainer glands because of corrosion.
This type pipe is commonly used in municipal systems and is usually buried. If corrosion is anticipated, then the installer may wrap (polyethylene encasement) the pipe to prevent corrosion. You can find that on the US Pipe website.
There is a basic gland ring supplied for MJ pipe joints that is not a restrained joint. It is designed to simply hold the gasket in place at the joint. There is also a gland ring for MJ pipe that has set screws in the gland which tightens down against the pipe to make it a restrained joint. There is also retainer glands such as Megalugs which also make it a restrained joint. The Megalug type restraints use a tapered wedge that tightens down to the pipe, which gets even tighter if the pipe tries to seperate. If basic MJ pipe is specified without specifying the need for restrained joints, then thrust blocks would be needed at changes in direction of the pipe.
Retainer gland: use not recomended under any circumstance, it is a regular gland with set screws. The set screws produce a point load which will crack Cast iron, split c-900 and can crack poor quality ductile. The set screws can slip under higher loads such during a water hammer event.
Wedge action restrained joint system: (as described by wwtpguru) I use all the time. Get the restrained joint pipe length calculator from the manufacturers to calculate how far the restrained joints need to be for a safe installation, in most cases you will need to restrain more than one length of pipe.
It is becomming more and more common to use mechanical joint restraints on pipe in lieu of concrete thrust blocks. I do not know if the work you speak of will be for private or municipal work. Some municipalities do not allow the use of mechanical restraints while some require both thrust blocks and restraints (overkill in my book). I have designed numerous domestic water and fire system lines in the Southern California region. If you intend to proceed with mechanical restraints, in lieu of thrust blocks, make sure the bell and spigots of the pipes also are restrained. There is a good restraint design program, available for free, from ebaa iron (probably the best manufacturer of these devices) at
We install 100 PSI plus irrigation systems using pvc pipe and ductile iron fittings with MJ restraints. In answer to your question whether concrete thrust blocks are needed you need to consider that the thrust blocks also serve as a backstop for the fitting which keeps the fitting from moving. If the restrained fitting moves, the immediate joint will not separate, but a joint of pipe upstream might separate. Remember that the pipes themselves are gasketed and pushed together without restraints and act like hydraulic cylinders when full of pressure. Usually, the trench where the pipe and fittings are installed is dug to provide adequate work space (to assemble the DI Fitting). I would highly recommend locking the fitting in place to restrict any movement, whether you use adequate, non-corrosive stakes, or concrete thrust blocks to fill the void between the pipe fitting and the trench wall. I hope this helps.
